Year Measure 1971 324.80557 1972 324.4067 1973 326.92493 1974 326.91918 1975 326.20496 1976 322.02484 1977 322.69376 1978 322.29265 1979 327.10993 1980 321.20187 1981 328.43583 1982 320.86816 1983 333.49144 1984 341.82617 1985 333.06226 1986 330.83097 1987 335.05688 1988 337.64811 1989 335.68926 1990 340.84876 1991 328.90624 1992 322.08447 1993 315.94675 1994 305.74923 1995 308.58323 1996 310.30646 1997 308.12729 1998 308.55834 1999 302.68001 2000 295.40884 2001 297.01284 2002 298.44357 2003 300.21055 2004 302.50057 2005 304.34727 2006 305.86631 2007 306.82633 2008 307.84652 2009 306.7412 2010 307.61335 2011 315.96325 2012 379.14814 2013 385.40022 2014 389.56739